1. Field of the Invention
The invention pertains to the field of blade tensioners. More particularly, the invention pertains to a blade tensioner with opposing spans coupled by a pin joint.
2. Description of Related Art
Chain tensioners in engines are used to control power transmission chains as the chains travels around a plurality of sprockets. The length of the chain varies as the temperature in an engine increases and as the chain wears. When a chain wears, the chain elongates and the slack in the chain increases. The increase in slack may cause noise, slippage, or tooth jumping between the chain and the sprocket teeth. If the increase of the slack of the chain is not taken up, by a tensioner, for example in an engine with a chain driven camshaft, the engine may be damaged because the camshaft timing is misaligned by several degrees due to slippage or tooth jumping.
The tensioning of the chain varies as the blade spring, the tensioner, and the chain wear. Preload, the nominal chain tension applied to the chain by a tensioner, under static conditions is imparted to the chain by the tensioner. In the case of a blade spring tensioner, the preload or nominal tension, under static conditions, decreases as the chain wears. The decrease in preload is caused by the blade spring becoming closer to its rest length as the tensioner extends to take up chain wear.
Prior art FIG. 8 is an example of a single blade tensioner. The conventional blade tensioner 110 includes a single blade shoe 111 made of resin having a curved chain sliding face 122 and numerous blade springs 121, preferably made of metallic material. The blade springs 121 are arranged in layers on the opposite side of the blade shoe 111 from the chain sliding face 122, and provide spring force to the blade shoe 111. The ends of each spring-shaped blade spring 121 are inserted in the indented portions 114 and 115, which are formed in the distal portion 112 and proximal portion 113 of the blade shoe 111, respectively.
A bracket 117 is provided for mounting the blade tensioner 110 in an engine. Holes 118 and 119 are formed in the bracket 117, and mounting bolts are inserted into these holes 118 and 119. A sliding face 116 contacts the distal portion of the blade shoe 111 and permits sliding. The sliding face 116 is formed on the distal portion of the bracket 117. A pin 120 supports the proximal portion 113 of the blade shoe 111 so that it may move in either direction. The pin 120 is secured on the bracket 117.
Simpson's U.S. Pat. No. 5,462,493 discloses a blade tensioner having two shoes and a blade spring, with one shoe imparting tension to a chain and overlapping the other shoe, which is connected to the blade spring. The two shoes are not directly connected to each other.
Simpson's U.S. Pat. No. 5,653,652 discloses a tensioner having two tensioner arms, with one tensioner arm imparting tension to a chain and overlapping the other arm. A hydraulic tensioner applies force against the free end of the overlapping tensioner arms. The tensioner arms may have blade springs. As one of tensioner arms applies a force to the chain, the other arm damps the movement of the first arm.
Tada's U.S. Pat. No. 6,044,020 discloses a blade type tensioner that includes a blade shoe with a chain sliding face, a blade spring for biasing the shoe toward the chain, and a bracket to rotatably support the fixed end of the blade shoe. The blade spring length is shorter than the chain sliding face. The first end of the blade spring is attached to the fixed end of the blade shoe and slidably contacts the distal end of the bracket, at a contact point located between the fixed end and the free end of the shoe.
Tada's U.S. Pat. No. 6,612,953 discloses a blade type tensioner that includes a blade shoe with a chain sliding face, a blade spring for biasing the shoe toward the chain, and a bracket to rotatably support the fixed end of the blade shoe. The blade spring length is shorter than the chain sliding face. The first end of the blade spring is attached the tip of the distal end of the shoe. The middle portion of the blade spring contacts the bracket.
Therefore, there is a need in the prior art for a blade tensioner that takes into account preload and chain wear.